The present invention relates to a rotor balancing system for turbomachinery which safely secures balancing rings to a rotor element while reducing windage effects caused by locating slots on the rotor element and to a method for positioning a balancing ring on a rotor element.
In rotating machinery, it sometimes becomes necessary to trim the balance of one of the rotor elements after the machinery has been initially balanced for assembly and has been operating in service. Typically, the machinery must be disassembled, completely or partially, to permit rebalancing or trim balancing of the offending rotor element. With aircraft gas turbine engines, it is desirable to be able to quickly and easily trim balance a compressor rotor after an airfoil has suffered foreign object damage and the damaged blade or blades have been blended in without removal of the engine from an aircraft.
It is known in the prior art to provide a construction for trim balancing a rotating piece of machinery which construction includes an annular rotor element having an outer face and an inner circumference, locating slots around the inner circumference of the rotor element, at least one annular groove within the rotor element behind the rotor element face, balance ring means positioned in the at least one annular groove, which balance ring means is split and has a weighted mass at one end thereof, and tab means connected by pin means to the balance ring means at the weighted mass end, which pin means extends through the rotor element locating slots, and the tab means being mounted on the pin means so as to be external of the rotor element. The construction also includes a casing structure means associated with the rotor element, which casing structure means has an opening therein through which tool means may be inserted to contact the tab means and deflect the pin means inward a controlled distance to free the pin means from the locating slots and permit a circumferential relocating of the balance ring means. Such a trim balancing construction is illustrated in U.S. Pat. No. 5,167,167 to Tiernan, Jr. et al.
One of the deficiencies of the Tiernan, Jr. et al. construction is that the locating slots act similar to rotating blades, turning and heating up the air in the cavities as the rotor element rotates. As a result, heated air is injected into the flow path. The mixture of hot cavity air and cooler flow path air reduces the overall fan efficiency. Additionally, the air pumping (windage) caused by the locating slots forces more air into the flow path. The air impinges with engine core flow reducing overall engine air flow. In addition the locating pin increases windage since it protrudes outboard of the balance ring and acts as a paddle turning air. Subsequently, this adds to the reduction in engine air flow.
Another deficiency in the present design is the ability to fine tune adjust the rotor trim balance. The anti-rotation pin slop and large disk engagement slot decrease the trim balance fine tune adjustment.